Some people are experiencing trouble, others are not. SP1 tightens security, but does a lot of it without you knowing, which makes it a pain to trouble shoot.
Microsoft has posted a technote regarding this issue to a degree which may alleviate a problem or two if you experience anything.
http://support.microsoft.com/?kbid=892500
It's working as designed according to MS, you think they would have warned people about the problem before they installed, rather than after.
Anyways, I have not experienced any problems, but others on here have and you can search for threads about it if you do find yourself with any issues after applying it.